They heard him chuckle, responding to the 911 call moments before he was killed by his own service revolver.

“Bus disturbance,” Francis was heard saying lightheartedly on the recording of the call from the early morning hours of July 2, 2008.

“Just screaming people.”

Francis, 60, decided to go to the scene alone, despite his proximity to the Belmont District police station, not realizing the danger he was in.

Within seconds, the 27-year Chicago Police veteran would be dead.

“He underestimated her,” Assistant Cook County State’s Attorney Jennifer Coleman said Wednesday of Johnson, the middle-aged woman accused of disarming Francis and killing the uniformed officer after he confronted her for the run-in she had with another woman on a CTA bus.

“He [Francis] underestimated the situation. He underestimated what she [Johnson] was capable of,” Coleman said.

Johnson was “aggressive, hostile and angry,” prosecutors told jurors in their closing arguments, describing Johnson’s actions against Francis and the four officers who came to his aid.

Johnson, 50, was acquitted of attempted murder and aggravated discharge of firearm charges for allegedly shooting at Francis’ colleagues, who returned fire and wounded Johnson.

Although he didn’t mention her reported mental illness, Assistant Public Defender Kulmeet S. “Bob” Galhotra said Johnson was “confused, distressed and in need of help” during her interaction with the other CTA commuter and her ensuing struggle with Francis.

Before Francis was shot, Johnson was seen holding her own breast, telling the commuter, who she didn’t know, “You made me this way,” Galhotra reminded jurors.

Johnson was pacing back and forth, stomping her feet and talking to herself outside the CTA bus she was seen walking in and out of, Galhotra said.